This is not actually the frame as such but the small strips of wood, often with a decorative groove or so, which surround the face of the door/window opening and conceal any gap between the door frame and the wall structure. An English carpenter calls this an architrave (pron. arkitrayv). Really I think either foder or omfatting might have covered this, foderomfattning sounds a bit tautological to me!
I presume a valvomfattning would fill a similar function and you could use the same translation (with more etymological logic, even!) , thought I can't imagine how you would actually machine one except out of plywood.